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MaddogK
August 17th, 2014, 21:33
Greeting all,
I'm hoping someone could help me out with a small headache I'm struggling with. I'm rebuilding one of my air files and tho I've got the max HP, engine drag (about 12% across the board), fuel consumption, prop speed and proper thrust I've discovered my fuel burn rates and HP go WAY below what they should be at cruise setting. My 'J' value is almost constant from 1800-2300, but tho my BHP is correct at full thrust at 2000 RPM I'm over 100HP under what my docs say my output should be. I don't have enough HP even if engine friction was 0. Since the 'J' value barely moves there's not much I can do with prop efficiency and there's not enough points in record 508 to compensate for the quickly falling HP.

Any ideas ?

Its a Curtiss D-12
carbureted
1:1 prop drive
470hp @ 2300 .58 lb per hr per hp << perfectly dialed in
415hp @ 2000 .54 lb per hr per hp << Should be 415/2000 but I'm getting 310hp BEFORE engine drag applies, about 105 pph burn rate
210hp @ 1850 <<< My eco cruise setting is 1850 rpm but 210 HP CANT be right, it should be about 385hp

Dev One
August 18th, 2014, 10:26
From my experience, 508 (which you have been playing with) & 509 affect output & hence fuel consumption, but also the curves for 511 & 512 will feedback & affect power & hence fuel consumption. Tricky one, just keep experimenting & good luck.
Mind you aircraft attitude & hence induced drag at certain speeds will mess up almost everything!!!
Keith

MaddogK
August 18th, 2014, 10:57
Thanks Dev one, thats exactly what I've been doing, but you're right- my CDi is high and I know it, it's an uncorrected number from my first iteration of this plane that was an arbitrary 'guess' to keep the engine/prop from overspeeding the A/C.

But guess what, after re-re-reading some of Jerry Beckwiths docs I think I see where I'm getting flogged- RPM (by virtue of the prop records 511 and 512) is needed to alter the J on the power and performance charts, but apparently the A/C MUST be moving to compute the J value and the HP as read by AFSD, but 'GASP'- I think Torque is derived directly from the engine performance records, AND

"torque times RPM divided by 5,252 -- to arrive at horsepower"

...Guess I'm chasing the wrong numbers, eh ?

:bump:

First thing I'm doing is dropping the CDi on the A/C (IIRC it's .05 or something) and flattening out the prop efficiency curve so I have more range on J.

Ivan
August 18th, 2014, 11:43
While I am pretty sure I can set up something like this for Combat Flight Simulator, there isn't a tunable fuel consumption that I have found. Not sure if this would be useful to you for FS 2004.

- Ivan.

MaddogK
August 18th, 2014, 11:48
While I am pretty sure I can set up something like this for Combat Flight Simulator, there isn't a tunable fuel consumption that I have found. Not sure if this would be useful to you for FS 2004.

- Ivan.

I'de appreciate it, but I'm gonna have another marathon session again tonight to see if my conclusion about torque is correct. If it is I should be able to manage the rest without putting you out, but I do appreciate the offer. You can adjust the fuel consumption by altering the engine efficiency datablock IIRC.

I'll report back tomorrow.

PS- you dont' have an accurate curve for a Reed R-1 airscrew, do you ? I have a NACA report but the data is hard to transpose into FS.

Dev One
August 19th, 2014, 04:33
Don't forget that the prop pitch angle can do a lot to restrict/overspeed the engine or aircraft airspeed, rather than play with the CDi all the time. J also then affected.
Keith

Ivan
August 19th, 2014, 05:55
Perhaps this thread would be helpful to you. It shows much of my basic method.

http://www.sim-outhouse.com/sohforums/showthread.php?77148-Engine-Performance-Tuning-Tutorial

IMHO:
Don't bother tuning the propeller to start. Even the airframe doesn't matter all that much to start.
Set it as a constant speed prop with enough reduction gearing to be able to achieve full engine RPM at the airspeed you are testing at.

That will show you what your actual engine performance (HP / Torque) is with just engine parameters.
Adjust the efficiency, torque drag, supercharger to get correct power at full RPM at SL and at altitude.

You can then adjust efficiency to get the proper cruise HP settings at less than full RPM and manifold pressure.
Be careful here because sometimes the numbers won't actually fit together.
I was once trying to tune a Wright R-2600 and found that once I had the correct cruise setting, I could just raise the manifold pressure at the lower RPM and actually get more power than I was getting at full RPM because the effiiciency was so much better at reduced RPM.

After the HP is set properly, you can adjust the propeller variables. If you mess with the propeller first, all the overspeed and lugging issues are going to mask what your engine settings should be giving you.

Just out of curiosity, What aircraft are you working on? (Simpler question than asking about all the engine specs.)

- Ivan.

MaddogK
August 19th, 2014, 08:28
Perhaps this thread would be helpful to you. It shows much of my basic method.

http://www.sim-outhouse.com/sohforums/showthread.php?77148-Engine-Performance-Tuning-Tutorial

IMHO:
Don't bother tuning the propeller to start. Even the airframe doesn't matter all that much to start.
Set it as a constant speed prop with enough reduction gearing to be able to achieve full engine RPM at the airspeed you are testing at.

That will show you what your actual engine performance (HP / Torque) is with just engine parameters.
Adjust the efficiency, torque drag, supercharger to get correct power at full RPM at SL and at altitude.

You can then adjust efficiency to get the proper cruise HP settings at less than full RPM and manifold pressure.
Be careful here because sometimes the numbers won't actually fit together.
I was once trying to tune a Wright R-2600 and found that once I had the correct cruise setting, I could just raise the manifold pressure at the lower RPM and actually get more power than I was getting at full RPM because the effiiciency was so much better at reduced RPM.

After the HP is set properly, you can adjust the propeller variables. If you mess with the propeller first, all the overspeed and lugging issues are going to mask what your engine settings should be giving you.

Just out of curiosity, What aircraft are you working on? (Simpler question than asking about all the engine specs.)

- Ivan.

I'm reworking my Fairey Fox biplane using the early 1920's Mk.1 specs- direct drive prop, NO blower or turbo (completely naturally aspirated carburated). It's here in the warbirds library. I have MUCH more early data than I did when I built it and really want to make it right before I rebuild the visual model. Heck, I have the authentic engine dyno data and prop data as well as the flight test data. I just can't make it work right in FS without lying to it to get the proper numbers. I'm completely hamstrung by the way FS calculates the J value, so with my limited RPM range and speed difference between the two with a 8.5-9 foot prop my J only gives me a range of 0.4 to work in.
:dizzy:
I'll re-read your link as I saw it a couple weeks ago but stopped reading after the first post when I saw you were messing a supercharged, constant speed prop airplane and didn't think what I was looking for applied to my issue. It's looking more and more like I'll need to have some sort low end manifold boost to get the HP and fuel burn rates where I need them. The engine data is hard to find for the early model but I'll be glad to provide and data/docs you may need to get an idea what I'm going for.

edit: I just had a thought, what if I try-
making it supercharged
critical altitude = 0 feet (sea level)
Max intake pressure 29.92 (may have to mess with it to get 29.92 @ full thottle with scaler)
...and define a boost scaler to get me my correct part throttle HP/fuel burn numbers

MaddogK
August 19th, 2014, 08:35
Don't forget that the prop pitch angle can do a lot to restrict/overspeed the engine or aircraft airspeed, rather than play with the CDi all the time. J also then affected.
Keith

Thats a thought- the one thing I don't have is the actual prop pitch of the A/C I'm working on. I'm assuming it's close to 21 but it could be much lower. Funny, when I dropped the CDi the J range greatly increased till I started pulling the prop efficiency and power required back into reality, now I'm back where I started but with a plane that'll glide much further.

Dev One
August 19th, 2014, 10:56
I must admit that on my aircraft I have no idea what the real world prop pitch is, & I dont know how near the FS algorithm is to prop theory! One just has to fiddle & hope to get the end result as near as possible. I'm fairly sure that the FS algorithms are a bit of a fudge - especially when one sees the very long list of items within some FDE'. I have been able on my last few a/c to reduce this down quite a bit, but they are GA 1930's & 40's types.

Jerry Beckwiths free FDWB gives one a bit of an idea, but I find the prop curves can have problems - again maybe aero theory not matching FS theory?
Keith

MaddogK
August 21st, 2014, 06:23
:jump:
Good news- I put a turbo in the FM and with some tweeking the HP is pretty dern close to what I need it to be but the fuel consumption is still a bit off. Luckily FS pins the BSFC to .49 pph per HP so with a fuel scaler I should be able to get the fuel numbers where I need them to be. You were right Ivan, there's noting in the air file that directly alters the fuel burn rates, I had observed the engine efficiency changing the fuel burn rates but didn't really notice the HP values were going up and I was compensating by making the prop loading heavier to keep the RPM down. By lying to FS about the turbo my HP stays authentic and the manifold pressure isn't dropping as fast as the non-turbo FM which seems to be keeping the HP up where it should be. I haven't looked yet but I'm hoping theres a turbo scaler in case altitude starts to throw my numbers off again.

Thanks guys for the ideas that led me to the right path, I think I finally have a handle on this problem.

Blood_Hawk23
August 24th, 2014, 02:23
I was messing with this a while back and came across this:

http://www.culverprops.com/pitchselection.htm

you can find more here:

http://www.homebuiltairplanes.com/forums/firewall-forward-props-fuel-system/1414-prop-pitch-calculator.html

not sure if it will help but might be useful.

MaddogK
August 25th, 2014, 07:35
I dunno what I did but it's back to the same as before, even with the turbo the cruise HP is way low ,I'm guessing because the manifold pressure is lower than it should be. Oh well, needed a break anyway- decided to rework the physical model instead and wouldn't you know it my source build is on a different computer that I boxed up 6 months ago and now it's dead. I had to pull the HDD and install it into my new PC so I can get my source models back, then I discover (or remember) that I did the final build in FSDS. Least I was smart enough to export every part as a DXF first. Hard to believe I built this thing 5 years ago.

Sheesh, when it rains, it pours.

Blood_Hawk23
August 25th, 2014, 10:28
I dunno what I did but it's back to the same as before, even with the turbo the cruise HP is way low ,I'm guessing because the manifold pressure is lower than it should be. Oh well, needed a break anyway- decided to rework the physical model instead and wouldn't you know it my source build is on a different computer that I boxed up 6 months ago and now it's dead. I had to pull the HDD and install it into my new PC so I can get my source models back, then I discover (or remember) that I did the final build in FSDS. Least I was smart enough to export every part as a DXF first. Hard to believe I built this thing 5 years ago.

Sheesh, when it rains, it pours.


Would you mind posting a copy of the air and cfg.

Dev One
August 25th, 2014, 10:28
I thought I had a problem yesterday after playing with my .air files & the changes would not work using the saved flight system. I then opened up using the standard Cessna then changed to my latest WIP & the changes worked OK - same in FS9 & FSX.

As for fuel consumption I'm a bit on the low side at the moment, but HP & Thrust, hence speeds are correct. I have also now been able to mess about with the curves in table 511 to achieve prop aerodynamic braking when reducing rpm.....I have made the curves 'avalanche' above a J value of 0.95, so that the efficiency falls almost immediately to -2.0 - this does mean making the values of J very close together (every 0.01) for a few values above 1.0.

I think tables 508 & 509 affect fuel consumption & power values - especially 509, but one must balance between the two. Thats my next experimentation!
HTH
Keith

BTW - those links for the prop values are not much good to me as they quote the prop pitch in inches, whereas MSFS quote them as degrees, but they do not specify at what prop dia that angle refers to. So I find it best to try different values in the .cfg & then empirically test!
K

Blood_Hawk23
August 25th, 2014, 12:36
google prop pitch calculator. there are a couple out there. other wise you would have to to do the math. if you can get all of the measurements that is.

you are using AirEd correct. you can also use airwrench, it will give you some info based on your changes to the air file. it the free version you can't make very many changes. Make sure your CFG matches the Airfile. I'm not sure about FSX but in some of the earlier FS sims the fuel settings need to match in order for everything to work right.

Does FSX have a FSedit? if so rename the cfg then run FSedit. it will make a new cfg based on the Airfile. Some things may be set wrong or missing but from that you can fill in the blanks.

without looking at the files that all I have. sadly I don't have FSX so I can't be a test pilot for you. hopefully there can be some inspiration in the what I have given.

Blood_Hawk23
August 25th, 2014, 13:05
Oh I forgot something.

If you search for a prop pitch calculator, make sure its for Aircraft and not Marine.

Blood_Hawk23
August 25th, 2014, 13:10
Try this...

http://www.warpdriveprops.com/propspd2.html (http://www.warpdriveprops.com/propspd2.html)

It has a converter deg to inch

MaddogK
August 26th, 2014, 07:07
Would you mind posting a copy of the air and cfg.

Sure, I'll try to get it posted tonight (provided storms don't knock out my power again), and BTW, I ran the calculators on the sites you provided below and my 'guess' was pretty dern close- the calculated pitch I should be running is 20.36 and I've been using 21 on this model. It's about as close to documented performance as it gets at wide open throttle, but part throttle performance is a complete headache because I can't keep manifold air pressure up where I need it so that HP and fuel burn rates remain as documented.

MaddogK
August 26th, 2014, 20:51
Would you mind posting a copy of the air and cfg.

Here's where I'm at ATM. I disabled the turbo because it stopped boosting low end manifold pressure and was causing some high end calibration problems, I also have the engine efficiency scaler set way too high @ 1850 trying to get the HP value up, but it's still not high enough and is causing unrealistic acceleration problems at takeoff. Fuel consumption isn't a real issue now that I know FS9 has pinned the fuel flow to .49 pph/hp so I can compensate with a scaler. My target performance specs are as follows:

2300 RPM / 155 mph / 470 HP @ sea level,
2100 RPM / 435 HP
2000 RPM / 425 HP
1850 RPM / 400HP (cruise setting) aprox 135 mph
Time to 2000 ft - 1.8 min , to 15000 ft - 21.5 minutes (max speed @ 14k-140MPH)
Range - 500 miles with 75 gallons fuel @ 130MPH
Service ceiling 17,000 ft.
This is a completely natural aspirated engine- NO turbo, NO supercharger, NO prop reduction gear, Carburated.
It should be noted that this aircraft was expected to have a range of 1750 miles with 175 gallons of fuel in the 1934 macrobertson race (Curtiss D-12 'Felix'). I calculated the optimum prop for a 2300 RPM motor at 8.25 feet, but looking at actual pics of the AC show it to be every bit of 9 feet or larger. I settled for 9 feet because I have the NACA test data for the 9 foot Reed prop on a Curtiss D-12 from the early 1930's so I thought it was a good match since Fairey mounted Reed props on this aircraft at that time, tho I gave up trying to reconstruct the prop tables in FS9 from the published test data curves. Trying to match the RPM to FS's 'J' variable was a bit beyond my math skills.

Lemme know if you see anything that I overlooked, or botched badly. I have until early October to wrap this up in order to get it qualified for our annual Macrobertson re-enactment. Thanks for looking.

Blood_Hawk23
August 26th, 2014, 21:36
First thing I see in the CFG is your entries need to be looked at. after the "=" you have spaces for some and no spaces for others. not sure if this matters but it might. I'm going to run them through a couple of programs and get some data. I'll post the pics provided I don't have any issues with my programs.

In the airfile is entry 509 needed? it refers to a turboprop.

1520- fuel injected?

turbo is still on in the airfile...

double check your fuel tanks for both air and cfg... they don't match

1178711788

Thats just looking at it. not sure if any of it is the culprit or not.

Blood_Hawk23
August 26th, 2014, 22:41
try upping the compression ratio to 6:1

oh here is a little calculator for CID
http://www.mk5cortinaestate.co.uk/calculator2.php

I find it handy. alot better then doing the math by hand. I like to double check them from time to time. you'd be surprised how often its overlooked. your CID was fine.

General characteristicsType: 12-cylinder liquid-cooled 60-degree V
Bore: 4.5 in (114.3 mm)
Stroke: 6.0 in (152.4 mm)
Displacement: 1,145 cu in (18.8 liters)
Length: 56.75 in (1441 mm)
Width: 28.25 in (717.5 mm)
Height: 34.75 in (882.6 mm)
Dry weight: 693 lb (314 kg)
ComponentsCooling system: Liquid-cooled
PerformancePower output: 443 hp (330 kW) at 2,200 rpm
Compression ratio: 6:1

Dev One
August 26th, 2014, 23:04
I find that 509 is needed for piston engines to correct for the ideal HP generated by the fuel - you can see the effect if you run AFSD -
In fact the title says 'per cyl'.
Keith

Blood_Hawk23
August 26th, 2014, 23:13
it helps if you read the info and see that it mentioned both recip and TP. I removed the entry and ran it in airwrench. I see the effects now.

i turned off the turbo in the airfile. I also turned off 1520.

i added the min gov rpm of 575 to both the air and cfg. don't know how that will effect you. you might notice it on the ground. not sure where the number came from but airwrench had it there even though its wasn't in the airfile or cfg.

the data i'm seeing seems to be close to your desired numbers. I have one more program that I can run it all through.

have you checked the flight dynamics? you might have too much drag. just a thought.

Dev One
August 27th, 2014, 01:14
One thing I noticed when I was creating my Miles M13 Hobby, was that the flight reports noted that the manifold pressure was positive 1 psi @ 1000' - this was obviously due to the position of the carb intake, so I had to make the turbo active but at a low pressure. Normal 'boost' pressure in FS for a non turbo engine is always negative. Just a thought.
As for range/fuel consumption - do you know at what altitude they flew for best range? That can make quite a difference.
Just been fiddling my values for my WIP Falcon six using both 508 & 509 as well as adjusting prop pitch & drag, to get fuel flow, HP, RPM & ASI near correct. Got to keep the altitude very low when checking all of these - keeping it above ground level gets interesting as well as trying to read all the parameters!
Keith

MaddogK
August 27th, 2014, 06:50
it helps if you read the info and see that it mentioned both recip and TP. I removed the entry and ran it in airwrench. I see the effects now.

i turned off the turbo in the airfile. I also turned off 1520.

i added the min gov rpm of 575 to both the air and cfg. don't know how that will effect you. you might notice it on the ground. not sure where the number came from but airwrench had it there even though its wasn't in the airfile or cfg.

the data i'm seeing seems to be close to your desired numbers. I have one more program that I can run it all through.

have you checked the flight dynamics? you might have too much drag. just a thought.

Hmm... well the turbo entry in the air file was set in that record when I was experimenting with adding a turbo late last week but I forgot to change it back when I removed the turbo from the CFG file. Supposedly FS9 overrides that setting in the air file with the CFG setting so I didn't think it critical to remove it at the time.

The compression of THAT particular engine in this aircraft is very specific- and set to the documented spec in the CFG file.

Fuel capacity in the air file is overridden by the CFG file (I'm told) but the documented performance is of a 75 gallon laden aircraft, 2 crew, and 2-220 lb bombs.

I'm unsure about the airframe drag, but it was stated many times in the docs I have that is was a very low drag aircraft, so I assumed a value slightly higher than the slipperiest aircraft at the time- the DH.88 Comet. (incidentally the value I started with was that of a DC-3). I think the value I'm currently using is somewhere between the two.

I imagine it's easier to lie to FS to get the proper performance but I'm trying to understand why the correct values don't work, so this is a re-learning experience for me as I haven't touched an air file in a few years. I've been working the prop tables for documented performance at wide open throttle so they should be pretty close, it's just that HP reported by AFSD at part throttle that drives me crazy as 1850 RPM cannot be used as a cruise setting with such a low HP value used by FS even tho it's historically accurate. There's NO possible way I'm going to get the expected range of 1750 miles @ WOT, and at service ceiling @ 1850 RPM I'll be lucky to remain airborne.

I guess I could overpower the engine to get the cruise HP desired, then gimp the WOT prop tables but I'm trying not to do that.

Blood_Hawk23
August 27th, 2014, 10:38
even airwrench gives conflicting results with regards to range. in it it gives less range at lower rpms. i think it could be the fixed prop. Maybe. it seems to be getting close to mach at the tip. i run an angle of 35 on my WWI ACs but all have this for the turbo

turbocharged= 1
max_design_mp= 29.000
min_design_mp= 12.000
critical_altitude= 100.000
emergency_boost_type= 0
emergency_boost_mp_offset= 0.000
emergency_boost_gain_offset= 0.540

here is what i run for my prop

[propeller]
propeller_type= 0
propeller_diameter= 9.000
propeller_blades= 2
propeller_moi= 12.697
beta_max= 35.000
beta_min= 35.000
min_gov_rpm= 600.000
prop_tc= 0.010
gear_reduction_ratio= 1.000
fixed_pitch_beta= 35.000
low_speed_theory_limit= 44.000

i haven't tried it on yours yet. it could make it worse for all i know. these are from my sopwith camel. other then prop dia all of my WWI ACs use the same. a few do have reduction gears.

i'm not sure how the other FS sims behave but cfs2 does some strage things with the airfile and cfg. In our case the player AC will use the entries that are in the cfg when they differ from the air file. but the AI it is the other way around. so you may never see the difference if it is a player only AC. there might not be any. just a thought.

i'm back to work for the next four nights. I hope that your able to figure it out.

Till Later,
John

MaddogK
August 29th, 2014, 07:03
even airwrench gives conflicting results with regards to range. in it it gives less range at lower rpms. i think it could be the fixed prop. Maybe. it seems to be getting close to mach at the tip. i run an angle of 35 on my WWI ACs but all have this for the turbo

turbocharged= 1
max_design_mp= 29.000
min_design_mp= 12.000
critical_altitude= 100.000
emergency_boost_type= 0
emergency_boost_mp_offset= 0.000
emergency_boost_gain_offset= 0.540

here is what i run for my prop

[propeller]
propeller_type= 0
propeller_diameter= 9.000
propeller_blades= 2
propeller_moi= 12.697
beta_max= 35.000
beta_min= 35.000
min_gov_rpm= 600.000
prop_tc= 0.010
gear_reduction_ratio= 1.000
fixed_pitch_beta= 35.000
low_speed_theory_limit= 44.000

i haven't tried it on yours yet. it could make it worse for all i know. these are from my sopwith camel. other then prop dia all of my WWI ACs use the same. a few do have reduction gears.

i'm not sure how the other FS sims behave but cfs2 does some strage things with the airfile and cfg. In our case the player AC will use the entries that are in the cfg when they differ from the air file. but the AI it is the other way around. so you may never see the difference if it is a player only AC. there might not be any. just a thought.

i'm back to work for the next four nights. I hope that your able to figure it out.

Till Later,
John

Between the two calculators you linked to earlier I'm able to plot out the speed/RPM curve I expect, and using the known formula for calculating the FS9 'J' value I plotted the expected values as well only to discover the range of 'J' from 108MPH to 156MPH to be less than .015, so with 156MPH @ 2300 being right on the money no amount of prop table tweeking is going to get me 125MPH @ 1850 RPM because manifold pressure is just too low @ 1850 to generate the expected 380HP.

I need to figure out how manifold pressure is calculated, THEN I might be able to get that elusive cruise speed setting to work right. Looks like I'm doomed to lie to FS9 and install a supercharger (the turbo is too weak), use wrong displacement and compression numbers, or something even more radical.
:banghead::banghead::banghead:

Aww carp, ;) this is how I started my journey but somehow talked my way out of it.
http://www.fsdeveloper.com/forum/threads/rpm-vs-hp-for-piston-engine.18243/

Dev One
August 29th, 2014, 11:11
By playing even further with table 511, you can get aerodynamic braking when closing the throttle!
For any J value above .95 with a positive efficiency value needs to be made negative - I've used -2.0 - & I've found that for my WIP aircraft that closing the throttle at 160 MPH (cruise speed) to the flaps operating speed of 100MPH, before modification took 55 - 60 seconds in level flight.
After modification this reduced to 25 seconds. This value was suggested after I queried a real pilot with a 172 in a forum question elsewhere at SOH.
I have also amended the curves lower down to get a better HP value & rpm during stationary run up & during take off. Fuel consumption also nearer the mark at cruise. Cruise drag value also tweaked to balance things out.

Keep fiddling, you will get there, although probably with less hair!
Keith

MaddogK
August 30th, 2014, 06:02
By playing even further with table 511, you can get aerodynamic braking when closing the throttle! For any J value above .95 with a positive efficiency value needs to be made negative - I've used -2.0 - & I've found that for my WIP aircraft that closing the throttle at 160 MPH (cruise speed) to the flaps operating speed of 100MPH, before modification took 55 - 60 seconds in level flight. After modification this reduced to 25 seconds. This value was suggested after I queried a real pilot with a 172 in a forum question elsewhere at SOH. I have also amended the curves lower down to get a better HP value & rpm during stationary run up & during take off. Fuel consumption also nearer the mark at cruise. Cruise drag value also tweaked to balance things out. Keep fiddling, you will get there, although probably with less hair! Keith Hmmm... Table 506. According to AAM "Affects manifold pressure. Sets throttle Idle stop and max MP wrt Induction Flow" It has 2 points creating a flat, linear 'curve'. I wonder...1 axis has got to be the throttle position but I'll bet the other is the induction flow percentage. Would be interesting to see if it'll work with more than 2 points in the graph.

EDIT : WOW, I'm onto something here. Adding a 3rd point in 506 lets me redefine the throttle curve, and 'fattening up' the low to mid range got me 12 MPH @ 1850 RPM over the untouched 506 curve. I also noticed my 'J' value has shifted -.15 across the board which it should do. I think Jerry's equation is missing a variable. My top speed hasn't changed but the low RPM power range has definitely been improved.

Dev One
August 30th, 2014, 10:11
Nice find - thanks for the idea, I will have to try it as I don't have it on my simplified listing.
Keith

Blood_Hawk23
August 31st, 2014, 02:53
sounds like your making progress.

here is an article to check out. It may have something usefull.

http://www.advancedpilot.com/downloads/prep.pdf

MaddogK
August 31st, 2014, 06:26
Nice find - thanks for the idea, I will have to try it as I don't have it on my simplified listing.
Keith

I stumbled on it by the description of the record in AAM, but it's probably not the best solution as I can't find any other aircraft in FS that has more than 2 points in this record, but the results are startling. I should however stress a small mistake in my above post about my shifted 'J' values, altering this record should NOT have altered the 'J' values in any way since 'J' is calculated strictly by RPM and A/C speed vs. prop diameter. I definitely have to look closer at this record or find the record that can alter 'boost gain'. I think I'll try inverting it to see what happens.

EDIT : EUREKA !!! Inverting 506 seems to have solved my dilemma- I've NOW got a MP of 21 @ 1850 RPM instead 10. My cruise speed 'magically' found itself just short of 5 MPH from where the docs say it should be. Now I can rework the numbers and hopefully get them to match the docs.

Thanks Blood_Hawk23, that IS an interesting doc. It's got some nice explanations of 'old school' tuning tricks we used to use on carburated engines before the computer management systems were widely used. I wish I had that chart of cylinder head temp vs. mixture years ago when trying to explain to a customer why their car ran like crap on the highway and why we had to rejet their carburator.

Blood_Hawk23
August 31st, 2014, 17:02
Well from one mechanic to another, your welcome. I hoped it has helped.

So the question now is has your range improved? The MP at 10 would explain alot. According to the doc it should have gone up atleast a little due to the slower RPM.

The trouble you've been having is why so many CFS2 designers use the stock AIR and CFG files. Very few can understand, let alone adjust the AIR files. It seems the Old programers GIGO (garbage in garbage out) still holds true. How were you able to change it?

If there is away to convert your AC to CFS2 I'd love to fly it.

MaddogK
September 1st, 2014, 04:09
Well from one mechanic to another, your welcome. I hoped it has helped. So the question now is has your range improved? The MP at 10 would explain alot. According to the doc it should have gone up atleast a little due to the slower RPM. The trouble you've been having is why so many CFS2 designers use the stock AIR and CFG files. Very few can understand, let alone adjust the AIR files. It seems the Old programers GIGO (garbage in garbage out) still holds true. How were you able to change it? If there is away to convert your AC to CFS2 I'd love to fly it. As an old mechanic I couldn't understand why manifold pressure was so low at idle and mid range but assumed FS was doing some 'behind the scenes magic', now that I think about it 506 being inverted makes a little sense, the air file I used was a donor that had a turbo and would need it that way for as a turbo would make the man pressure go positive at higher RPM's- a naturally aspirated engine would never go positive while it's running. I would guess the reason why default NA FS9 A/C don't even have that record is because FS does assume it's own correct record 506 if it's missing. I changed it simply by using AAF (aircraft airfile manager) and transposing the 'Y' values from each end of the graph. Inserting the third point in the graph was done with Jerry Beckwith's Airupdate utility and notepad.

And YES, cruise range increased at least 100% simply because the engine is producing more torque to turn the prop at cruise setting, and part throttle airspeed increased 30%. Maximum airspeed is unaffected, and I would assume that climb rate and ceiling are also untouched as well but can't confirm that until I do some more testing after I tweek the prop tables some more. Since I'm rebuilding the visual model anyway I'll see what I can do to build a CFS2 version, but it's been at least 10 years since I've built anything for CFS2.

Dev One
September 1st, 2014, 04:15
506 is also listed in the templates within FS9 listing - I found it in the single engine HP template.
Interested in how you did the 3rd point insert though, so I will try doing it with Jerrys FDWB.
Keith

MaddogK
September 1st, 2014, 06:38
506 is also listed in the templates within FS9 listing - I found it in the single engine HP template.
Interested in how you did the 3rd point insert though, so I will try doing it with Jerrys FDWB.
Keith

It was pretty simple- using the utility just export as a txt file, edit into record 506 another X,Y coordinate and a value, save the txt file and re-run the utility to recompile the air file.

fliger747
September 14th, 2014, 14:36
A couple of comments:

Fixed pitch props are quite a bit more difficult to work with than constant speed props in setting up an FS engine as you have added an extra variable.

Older piston engines experienced a lot of delivered power loss at high we RPM values due to internal losses, lubrication slinging being one of the real culprits. Even the relatively late and sophisticated R2800 gained quite a bit more than 100 HP between the B and C series just due to an improved oil scavenging system, plus another useable 100 RPM. For FS piston engines the shape of the Friction per cylinder curve (wish there were more points) can be tuned to approximate the HP output ratio vrs RPM. Of course the fixed pitch prop curves make life extra exciting and the overall HP of the engine must be re adjusted.

Specific Fuel Consumption: A value of .49 would be low for an engine of this era as this was typical of WWII high performance engines. Modern general aviation engines tend to do a bit better with values somewhere around .43 lb/hr/hp or so. The R985 I am currently flying in the DHC Beaver relies quite a bit on mixture enrichment for cylinder cooling at higher power settings.

Not sure that a min governed RPM has any effect for a fixed pitch prop. Not that it should have too much effect, but wooden props tend to have low MOI values, the main reason they are not found much on gen av aircraft these days has to do with the constant maintenance required.

Fun Project! Cheers: Tom

MaddogK
September 16th, 2014, 07:08
A couple of comments:

Fixed pitch props are quite a bit more difficult to work with than constant speed props in setting up an FS engine as you have added an extra variable.

Older piston engines experienced a lot of delivered power loss at high we RPM values due to internal losses, lubrication slinging being one of the real culprits. Even the relatively late and sophisticated R2800 gained quite a bit more than 100 HP between the B and C series just due to an improved oil scavenging system, plus another useable 100 RPM. For FS piston engines the shape of the Friction per cylinder curve (wish there were more points) can be tuned to approximate the HP output ratio vrs RPM. Of course the fixed pitch prop curves make life extra exciting and the overall HP of the engine must be re adjusted.

Specific Fuel Consumption: A value of .49 would be low for an engine of this era as this was typical of WWII high performance engines. Modern general aviation engines tend to do a bit better with values somewhere around .43 lb/hr/hp or so. The R985 I am currently flying in the DHC Beaver relies quite a bit on mixture enrichment for cylinder cooling at higher power settings.

Not sure that a min governed RPM has any effect for a fixed pitch prop. Not that it should have too much effect, but wooden props tend to have low MOI values, the main reason they are not found much on gen av aircraft these days has to do with the constant maintenance required.

Fun Project! Cheers: Tom

Ya, the 'assumed' fuel consumption of FS9 is a bit low compared to the actual dyno data, but I can fix it with a scaler. Now that I've seen what I can get away with in the prop curves I'm pretty close to where the NACA data says I should be, and the rest I think I can guesstimate by the 'feeling' in-game. Oh, I can't even guess at the prop MOI as it was a forged aluminum prop- very cutting edge for it's time (only a couple years from it's patent date).

Who can actually point at me and say I'm outright wrong when dealing with a very limited number of 90 year old aircraft, but I'll take every criticizm under advisement. The previous model was RTW committee approved so it was pretty close, but after looking at it again a few years later all I can think of is "what was I thinking, this isn't even close".
;)

fliger747
September 23rd, 2014, 13:03
The aluminum props have a higher moment value but do have advantages where it comes to maintainance, durability and precision of manufacture. A friend has a wooden prop on her Pacer, but she, being and a&p plus IA, is willing to put up with the hassles for her specific application. Earlier engines suffered from les sophisticated carburation and exhaughst, poorer fuels etc, so a lower fuel efficiency would be expected. It was appreciated that extra rich mixture was beneficial for cooling and instrumentation was certainly not available to monitor much besides oil and coolant temperatures.

The RTW folks mostly look at top speed....

regards. Tom